Gap junctions are known to be essential for the survival and metabolic homeostasis of the eye lens. We as well as others have revealed a novel feature of the lens connexin involved in promoting epithelial-fiber differentiation and lens development. Our long-range goal is to understand the molecular mechanism(s) and functional significance of connexin molecules in lens development and homeostasis. The objective of this application is to understand the mechanistic roles of Cx50 in cell differentiation, and in lens growth and development. The central hypothesis are: (1) Cx50 is functionally involved in lens differentiation by interacting with cell cycle regulators, a role independent of gap junctions;(2) the localization and stabilization of Cx50 in lens fibers is facilitated by MIP. Two specific aims will be pursued: 1). Define the molecular mechanism of the PEST domain of Cx50 in epithelial-fiber differentiation and lens development. 2). Determine the functional significance of the interaction of MIP and Cx50. One of the innovative aspects is that this proposal aims to dissect the molecular mechanisms of an unconventional function of lens connexin. Moreover, the research program will be accomplished using our established avian retroviral approaches as the principal tool for experimental manipulations of primary chick lens cultures as well as in vivo chick lenses. More importantly, the findings obtained from chick lens will be validated and complemented by proposed studies using wild type and knockout mouse models. It is our expectation that our experimental findings will provide a molecular basis for understanding the functional significance and regulatory mechanisms of Cx50 in differentiating lens fibers and are expected to have a major positive impact on defining the process by which lens connexins are involved in lens growth and development. The outcomes of our research will be significant because the new knowledge discovered will contribute to a broader understanding of mechanistic aspects of epithelial-fiber differentiation and lens development. Public health relevance: Cataracts are one of the most common eye diseases and also one of the leading causes for blindness worldwide. The proposed research activity will help understanding the biological process of lens function and formation and, in a long run, should make novel contributions to strategies for treatment of cataracts, and to new ideas and potential targets for drug discovery and development.